A major, immunodominant, 47,000 (47K) MW surface immunogen of Treponema pallidum was identified using functionally-defined anti-T. pallidum monoclonal antibodies. It may represent the major immunogen of T. pallidum. The aim of this proposal is to further examine the biological activities of both the "native" 47K immunogen as well as antibodies elicited against it, and to assess their overall role(s) in the pathogenesis and immunology of treponemal infection. The 47K surface immunogen will be affinity purified from in vivo- or in vitro-cultivated T. pallidum using monoclonal antibodies, and animals will be immunized. The antibody response in animals immunized with 47K immunogen will be assessed using radioimmunoassay, microhemagglutination assay for T. pallidum, indirect immunofluorescence, radioimmunoprecipitation, Western blotting, T. pallidum immobilization assay, blockage of T. pallidum attachment to host cells in vitro, and in the in vitro-in vivo neutralization test of Bishop and Miller. Animals exhibiting strong humoral responses will be challenged with viable T. pallidum to assess the vaccinogenic potential of the purified 47K immunogen. Simultaneously, anti-47K monoclonal antibodies will be used in passive immunization studies with rabbits or hamsters. The complete primary amino acid sequence for the 47K immunogen will be deduced from studies combining monoclonal antibody immunoaffinity purification, N-terminal amino acid microsequencing, and recombinant DNA techniques. Polyclonal or monoclonal anti-idiotypic antibodies, initially raised against the idiotype of anti-47K monoclonal antibody 11E3, will be used in attempt to elicit an anti-T. palldium response in animals never exposed to T. pallidum. In ongoing studies, monoclonal antibody affinity purification of the 102K, 84K, 54K, 53K, 52K, 32K, 29K, and 24K immunogens of T. pallidum will also be attempted. Production of anti-T. pallidum monoclonal antibodies for the isolation of monoclonal antibodies directed against the 36K, 34K, and 13K immunogens will continue. The study attempts to narrow the information gap regarding the role of the prospective immunogens of T. pallidum, and the antibodies they elicit, in the immunopathogenesis of syphilis.